Among different types of solar cells, the multijunction solar cell is the most efficient solar cell and is therefore suitable for concentrator solar cell batteries. Several solar cell batteries having the III-V multijunction solar cells have been known (e.g., see PTLs 1 and 2). FIGS. 11 to 14 illustrate schematic views of cross-sectional structure of conventional solar cell batteries having the III-V multijunction solar cells.
FIG. 11 is a first example of a conventional solar cell battery (see PTL 1). Solar cell battery 100 illustrated in FIG. 11 includes optical component 110 for concentrating sunlight and back sheet 140. Optical component 110 is formed from a Cassegrain glass lens. In a part of the glass lens, recess 113 for placing therein solar cell 120 is formed.
Back sheet 140 is bonded to optical component 110. Back sheet 140 includes circuit board 150 and adhesive layer 155. Circuit board 150 includes insulator 153 and conductor 154. Solar cell 120 is electrically and physically connected to electrode part 154A and 154B of conductor 154 by first connecting part 124A and second connecting part 124B, respectively.
FIG. 12 is a second example of a conventional solar cell battery (see PTL 2). Solar cell battery 200 illustrated in FIG. 12 includes an optical component for concentrating sunlight and primary mirror 230 integrally formed with the optical component. The optical component is formed from a Cassegrain glass lens.
Primary mirror 230 includes two metal films 231 and 234 arranged with gap 237 in between. Primary mirror 230 has a bowl shape. The flat part at the bottom of primary mirror 230 has opening 239. Opening 239 is a path for concentrated sunlight. Solar cell 220 for receiving sunlight passed through opening 239 is fixed outside of the bottom of primary mirror 230. Solar cell 220 includes electrodes on both sides, one of which is connected to an interconnection line by die-bonding and the other is connected to an interconnection line by wire bonding.
FIG. 13 illustrates solid light-transparent optical panel 300 which is an array of solar cell batteries 200 illustrated in FIG. 12. Optical component 210 in solar cell battery 200 is hexagonal. Optical components 210 are disposed next to one another to constitute one panel.
FIG. 14 illustrates concentrator solar collecting unit 400C which is an array of solar cell batteries 200 illustrated in FIG. 12. In concentrator solar collecting unit 400C, the above-described two metal films 231 and 234 of solar cell battery 200 constitute two electrodes, i.e., the P-side electrode and N-side electrode, respectively. The P-side electrode on one of two adjacent solar cell batteries 200 and the N-side electrode on the other of the two adjacent solar cell batteries 200 are electrically connected. Concentrator solar collecting unit 400C is composed by connecting pairs of solar cell batteries 200 in series. Power generated at concentrator solar collecting unit 400C is extracted to outside by socket connector 420. Other related techniques are also presented (for example, see PTLs 3 to 6). For example, PTLs 3 to 5 disclose a solar cell battery in which sunlight concentrated by a lens enters a multijunction solar cell device fixed to a substrate having heat dissipation property. PTL6 discloses a solar cell in which a first electrode in square U shape having one end attached to the surface of the P-type semiconductor is provided on an insulating film covering the side surface of the N-type semiconductor and the end of the back surface and is connected to the bus bar on the front surface. The inventions according to PTLs 3 to 6 have concerns in heat dissipation property and others.